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Subjectefisubsys_init takes more than a few milliseconds
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Dear Ard,


According to `initcall_debug`, `efisubsys_init` takes more than a few
milliseconds to execute on a Dell XPS 13 9370 (Intel(R) Core(TM)
i7-8550U CPU @ 1.80GHz).

> ```
> […]
> [ 0.144474] calling efisubsys_init+0x0/0x2cf @ 1
> [ 0.144474] Registered efivars operations
> [ 0.173690] initcall efisubsys_init+0x0/0x2cf returned 0 after 27343 usecs
> […]
> ```

To get a vanilla Linux kernel to boot in well under one second, it’d be
nice if the time could be improved. Do you know, why it takes so long?

According to `bootgraph.py` from pm-graph [1][2] it takes even a little
longer.

> efisubsys_init: start=690.841, end=720.493, length(w/o overhead)=31.250 ms, return=0

There are several dozen calls to `virt_efi_get_next_variable()` all but
one taking around 0.335 ms. This path needs to be optimized. Is that
possible?

To reproduce this, clone the pm-graph repository [2], use `sudo
./bootgraph.py -f -fstat -maxdepth 10 -manual` to see what to add to
`/boot/grub/grub.cfg`. Then reboot, and execute `sudo ./bootgraph.py -f
-fstat -maxdepth 10`.

If your system is powerful enough, you can use a higher maximum depth. I
didn’t get around how `-cgfilter` works to get smaller HTML files.


Kind regards,

Paul


[1] https://01.org/suspendresume
[2] https://github.com/01org/pm-graph

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